change ~ experimental inclusion of meta.mainFilename (+ test mods)

- add `meta.mainFilename` to Platform.Adapter
- note: associated `OSPaths.main()` function is tested but undocumented
- primarily for ESM platform testing if ESM script name hack
- will be needed for XDGAppPaths (but not for OSPaths)

src/esm-wrapper/index.js

@@ -4,6 +4,12 @@
 import _ from '../index.js';
 // note: not usable by `deno`;
 //   ...`deno` is unable to load (the CJS module) '../index.js' via import => `'../index.js' does not provide an export named 'default'`
+import { adapter } from '../platform-adapters/node.js';
+
+// re-define `meta.mainFilename` adapter for ESM scripts
+// HACK: `process._eval` is undocumented; used here as evidence of `node -e ...` differentiating between immediate eval vs file-bound scripts
+// eslint-disable-next-line functional/immutable-data
+adapter.meta.mainFilename = typeof process._eval === 'undefined' ? process.argv[1] : '';
 
 const default_ = _;
 export default default_;

src/lib/OSPaths.test.ts

@@ -8,7 +8,7 @@ type moduleInternals_ = typeof module_ & {
 };
 
 test('api', (t) => {
-	const api = ['home', 'temp'];
+	const api = ['home', 'temp', 'main'];
 
 	t.is(typeof module_, 'function');
 	t.deepEqual(Object.keys(module_).sort(), api.sort());

src/lib/OSPaths.ts

@@ -9,6 +9,7 @@ export type OSPaths = {
 	(): OSPaths;
 	readonly home: () => string | undefined;
 	readonly temp: () => string;
+	readonly main: () => string;
 };
 
 const { env } = process;
@@ -85,6 +86,8 @@ class _OSPaths {
 		OSPaths.home = extension.home;
 		OSPaths.temp = extension.temp;
 
+		OSPaths.main = () => adapter.meta.mainFilename;
+
 		return OSPaths;
 	}
 }

src/platform-adapters/_base.ts

@@ -2,6 +2,7 @@
 export namespace Platform {
 	export type Adapter = {
 		readonly env: { readonly get: (_: string) => string | undefined };
+		readonly meta: { readonly mainFilename: string };
 		readonly os: { readonly homedir?: () => string; readonly tmpdir?: () => string };
 		readonly path: {
 			readonly join: (..._: readonly string[]) => string;

src/platform-adapters/deno.deno.ts

@@ -15,6 +15,7 @@ export const adapter: Platform.Adapter = {
 	env: { get: Deno.env.get },
 	// Deno (as of v1.6) has no built-in implementation for homedir() or tmpdir()
 	os: {}, // * module is tolerant of missing homedir()/tmpdir() functions
+	meta: { mainFilename: Deno.mainModule },
 	path,
 	process: { platform: Deno.build.os },
 };

src/platform-adapters/node.ts

@@ -9,6 +9,9 @@ export const adapter: Platform.Adapter = {
 			return process.env[s];
 		},
 	},
+	meta: {
+		mainFilename: process.mainModule?.filename || '',
+	},
 	os,
 	path,
 	process,

test/integration.test.js

@@ -26,7 +26,7 @@ const settledSupportForESMs =
 // Integration tests
 
 test('api', (t) => {
-	const api = ['home', 'temp'];
+	const api = ['home', 'temp', 'main'];
 
 	t.is(typeof module_, 'function');
 	t.deepEqual(Object.keys(module_).sort(), api.sort());